As known in the weaving art, a warp yarn drive moves warp yarns in order to reverse the shed and thus accomplish the interweaving of fabric in a loom. The weaving of material in a loom is accomplished by means of a suitable plurality of heald frames having eyes through which the warp yarns run. The heald frames are hinged at their bottom ends and, if the frames are long, they are also hinged at their bottom middle portion to respective bell cranks, suitable for converting the movement of a dobby into the vertical reciprocating movement of the heald frames along their side vertical guides. Inasmuch as the motion transmitted by a bell crank takes place in an arcuate trajectory and therefore clearly cannot be perfectly vertical, like, the reciprocating movement of the heald frames along vertical guides, the hinging of the heald frame to its respective bell crank is accomplished through short connecting rods which make compensation possible for the rotation of the bell cranks.
According to the present state of the art, one end of each bell crank is hinged to a connecting rod and the opposite end is provided with an elastically-closing hook suitable for cooperating with a pivoting pin supported under the heald frame.
Unfortunately, the prior art has a very serious drawback in that hooking all connecting rods to their respective pivoting pins requires an extremely long time, is expensive and is very difficult. Hooking all the connecting rods requires an attending operator to maneuver in a very uncomfortable position under the loom, in order to cause the individual connecting rods to pivot until their hooking is accomplished.
In order to overcome this drawback, complex mechanisms have been provided which are suitable for simultaneously hooking and disengaging all of the connecting rods, as well as keeping them in their optimal position so the above operations may be performed. But these measures are of considerable structural complexity and are a great financial burden so as to prevent this solution from becoming successful at a commercial level.